*276 The ffomologies of the Motor Area 



The cortex marked Ectosylvian B is of another type ; it is possessed of a fair fibre-wealth, but 

 contains no elements of large size. Its cells are divisible into the standard seven laminae, and 

 layers of moderately large external and internal pyramidal cells are discernible. 



FRONTAL CORTEX. 



The area marked frontal does not exhibit any special features, and it is not easy to find the 

 boundary between it and the other areas, save the motor, with which it comes in contact. 



LOBUS PYRIFORMIS. 



In the lobus pyriformis I have mapped out that cortex covered by a lamina medullaris externa, 

 and the layer of large polymorphous elements we are familiar with from our study of the brains of 

 other animals. 



PART II. 



A CONSIDERATION OF THE FUNCTIONS AND HOMOLOGIES OF THE AREAS 



HEREIN DESCRIBED. 



MOTOR OR CRUCIAL CORTEX. 



IN discussing the area designated crucial or motor, two important points stand out for con- 

 sideration ; one turns on experimental physiology and the question whether this field is the 

 functional equivalent of the motor area, as defined by Professors Sherrington and Grimbaum in 

 the anthropoid ape, and by myself in the human being ; the other pertains to comparative 

 anatomy, and concerns the fissural and gyral homologies of the cruciate region. These points will 

 be dealt with in turn. 



Looking back on the observations of those pioneers in experimental physiology who employed 

 common members of the carnivore family in ascertaining the results of cerebral excitation, we 

 notice, at once, that the cortex they found responsive, belongs to what we may call the cruciate 

 zone ; and, needless to add, the discovery of the excitability of this particular cortex was the pre- 

 liminary step in the acquirement of our present fund of information concerning the motor area. At 

 a later date, the recognition of " giant cells " in the same part brought confirmation, perhaps 

 inadequately acknowledged and appreciated, to the physiological results. But in precision of topo- 

 graphical localisation, I venture to say, these combined results have been left incomplete. In 

 particular, doubt is cast on the correctness of the earlier physiological experiments by the recent 

 researches of Professors Sherrington and Grunbaum, which show that the motor area is less 

 extensive than was previously thought, an amendment we must attribute to the employment of 

 improved methods of excitation. In substantiation of Professors Sherrington and Griinbaum's results 

 I have examined the brains of some of the animals (anthropoid apes) the} 1 had previously experi- 

 mented upon, and I have demonstrated that the excitable cortex is endowed with so many distinctive 

 structural qualities that its extent is as easily defined on the histologist's bench as on the 

 operating-table. Further, I have offered strong reasons for assuming that a similar condition of 

 affairs obtains in the human brain ; more, the present research makes it almost certain that the 

 same applies to many lower animals. I submit therefore, that the area I have described, and 

 marked " motor " in the accompanying diagrams, the area which, at any rate, in the case of Felis 

 and Canis possesses "giant" cells homologous to the cells of Betz, as well as a "motor" arrange- 



